Panel type, replaceable air filters are widely used in forced air heating and air conditioning systems. These filters often comprise a pad of air-permeable filtering material made of fiberglass or other suitable material. This pad is mounted in a frame, usually along with a reinforcing metal grid. The frame then is placed in the return air duct for the forced air system to remove dust particles and the like from the air flow. In time, the dust build-up on the filter becomes sufficient that the filter needs to be replaced or cleaned. The most popular filters are simply discarded and replaced with new filters. Consequently, they are inexpensively made, with the bordering frame for holding the metal support grid and the air-permeable filter pad being made of lightweight cardboard or the like.
There also is a large market for various products used to mask and control unwanted odors in homes and work places. Such products typically include air freshener sprays, blocks, electrically operated scent dispensers, candles, wicks, potpourri and the like. With all of these products, a number of drawbacks exist. With sprays, it is necessary to dispense the spray by hand in each room or area where the odor control is desired. With wicks, blocks, plug-in devices and the like, a number of them must be placed throughout the space in which the odor control is desired, in order to obtain the desired results. With all of these products, however, the benefits are relatively expensive and short-lived.
Attempts have been made to incorporate the release of odor control scents into the air handling system of furnaces and air conditioning systems. Three patents directed to a combination of scent release and air filtration are the patents to Ward U.S. Pat. No. 4,604,114; Fulmer U.S. Pat. No. 4,875,912; and Kappernaros U.S. Pat. No. 4,959,087.
The Ward patent is directed to a fragrance scented air filter, in which the otherwise standard disposable air filter includes two solid rods of scented material spanning the frame across the path of the air moving through the filter. The air which passes adjacent these rods absorbs the fragrance, which then is distributed by the air handling system in the building with which it is used.
The device of Fulmer places a scented evaporant packet in a cut-out portion of the filter, typically near a corner. A foil is placed over the evaporant packet; and when this foil is partially or fully removed, the evaporant is exposed to the air flowing in the return air duct. This packet, however, blocks the portion of the filter where it is placed.
The device shown in the patent to Kappernaros is an elongated bar of impregnated filter material, which is placed in a formed pocket on the edge of the frame around the air filter. A tear strip is provided over the material to expose various portions of the bar for scent release into the air stream passing through the filter.
The scented rods of Ward, and the packet of Fulmer are placed directly in the normal air path through the filter. Consequently, the area which is occupied by these devices effects a corresponding reduction in the air flow which passes through the filter. As a result, the area which is occupied by the scent releasing devices of Ward and Fulmer necessarily must be kept to as small a percentage of the overall area of the filter surface as possible. Since these devices also are placed in the main air flow path of air through the filter, they also are subjected to the maximum air flow through the filter; and therefore, the scent dispensing members must be fabricated to have a considerably lower volatility than would be necessary if they were not placed in the main air flow path.
The device of the Kappanaros patent does place the scented material out of the main air flow path of the filter. This device, however, requires a portion of the frame around the filter material to be enlarged to form the pocket in which the scent bar is placed. In addition, air flows past only one edge of the scent bar, the bulk of which is embedded in the frame of the air filter, in a position which prevents air from passing around it or through it.
In addition to providing scents for masking and controlling odors, interest also has been shown in dispensing anti-bacterial and/or anti-fungal agents into the duct work of a forced air heating or cooling system, for controlling bacteria, fungi and molds. Such materials also may be made in a form which sublimates or volatilizes as air passes over them, and can be formulated to function in the same manner as the release of scents described above in conjunction with the Ward, Fulmer and Kappanaros patents.
Accordingly, it desirable to provide an air filter system for use with a forced air heating or air conditioning system, which may be used to dispense scents or anti-bacterial and anti-fungal agents, without impairing the air flow through the filter, and without requiring dimensional modifications of the mechanical configurations of replaceable filters.